1. Field of the invention
The present invention relates to water based multicolor paints consisting of a dispersion of aqueous colored globules in aqueous dispersing medium.
2. Description of prior art
Multicolor paints consisting of water based dispersions of colored globules in a dispersing medium containing film forming material were first disclosed in U.S. Pat. No. 3,458,328. According to this patent, pigment containing hydrophilic colloids are reacted with insolubilizing medium to obtain colored hydrated gel-like precipitates that are non soluble in surrounding dispersion medium. The insolubilizing agent contained in the insolubilizing medium is of non-colloidal nature such as, e.g., Ca or Al cations, borates etc.
The thus obtained reaction products, i.e. the colored gels, have inherent limitations in membrane strength that make them unsuitable for application with brush or roller and that bring to stability problems of the precipitates if the water content of the composition exceeds critical values.
European Patent appln. No. 89830468.8 discloses a coating composition as obtained according to above cited U.S. Pat. No. 3,458,328, modified in that the film forming materials are resins having average particle size exceeding 2 .mu.m. While these compositions are suitable for application by brush or roller, they still have inherent drawbacks of long term stability at high dilution rates. U.S. Pat. No. 4,376,654 discloses a process for preparing multicolor aqueous paints wherein required colored gel precipitates are obtained by reacting two colloids that are also ionic and opposite in charge. This method has the drawback of being much more expensive than previous ones, where metal cations were used. Moreover, it is more difficult to control correct insolubilization with colloidal solutions than with metal salts solutions, the latter reactants concentration being more easily detected.
U.S. Pat. Nos. 5,123,963 and 5,125,972 disclose a preparation for multicolor aqueous coating compositions providing reactions between colored colloids and Al cations wherein, in order to obtain the required stability and resistance for brush application, the amount of reactant is such as to obtain hard and substantially non-hydrated colored precipitates, suitable to maintain the shape obtained after extrusion of the colored colloids in the insolubilizing medium.
While these products have a good stability at high dilution rates, they are not suitable for brush application because of their skidding on smooth surfaces. Moreover, the obtained precipitates, being dehydrated, have hard consistency, in order to substantially retain their original shapes (e.g. drop, star and so on) and their ratio with respect to dispersing medium is particularly low. Because of these limitations, the colored globules of these coating compositions do not provide a continuous multicolor coating film on the substrate, as provided by other state-of-the-art paints.